Japanese non-examined Patent Application Publication No. 2007-326168 discloses a hammer drill having a torque limiter. The torque limiter is provided with an intermediation gear actuated by a driving gear; a driven flange including a plurality of fear cam portions; balls held in a plurality of holding holes formed on the intermediate gear with a predetermined interval in a circumferential direction; a pressing plate, and a disc spring pressing the pressing plate.
While the hammer drill is working, in a state that the torque exerted on a hammer bit is less than the predetermined threshold, the pressing plate presses the intermediate gear against the driven flange by means of a biasing force of the disc spring and the intermediate gear and the driven flange are rotated integrally, thereby a torque of the intermediate gear is transmitted to the driven flange. On the other hand, in a state that the torque exerted on the hammer bit exceeds the predetermined threshold, since the ball moves over the cam portion against the biasing force of the disc spring, the pressing plate is pushed and the pressing to the intermediate is cancelled, thereby a transmission of the torque from the intermediate gear to the driven flange is cancelled.